Generally, multiple layer glass panels refer to a laminate comprised of a monolithic interlayer or interlayer sandwiched between two panes of glass. The laminated multiple layer glass panels are commonly utilized in architectural window applications, in the windows of motor vehicles and airplanes, and in photovoltaic solar panels. The first two applications are commonly referred to as laminated safety glass. The main function of the interlayer in the laminated safety glass is to absorb energy resulting from impact or force applied to the glass, keep the layers of glass bonded even when the force is applied and the glass is broken, and prevent the glass from breaking up into sharp pieces. Additionally, the interlayer generally gives the glass a much higher sound insulation rating, reduces UV and/or IR light transmission, and enhances the aesthetic appeal of the associated window.
The interlayer is generally produced by mixing a polymer resin such as poly(vinyl acetal) (poly(vinyl acetal)) with one or more plasticizers and melt blending or melt processing the mix into a interlayer by any applicable process or method known to one of skill in the art, including, but not limited to, extrusion. Other additional additives may optionally be added for various other purposes. After the monolithic interlayer is formed, it is typically collected and rolled for transportation and storage and for later use in the multiple layer glass panel, as described below.
The following offers a simplified description of the manner in which multiple layer glass panels are generally produced in combination with the interlayers. First, at least one monolithic interlayer is placed between two substrates and any excess interlayer is trimmed from the edges, creating an assembly. It is not uncommon for multiple interlayers to be placed within the two substrates creating a multiple layer glass panel with multiple interlayers. Then, air is removed from the assembly by an applicable process or method known to one of skill in the art; e.g., through nip rollers, vacuum bag, vacuum ring, or another de-airing mechanism. Additionally, the interlayer is partially press-bonded to the substrates by any method known to one of ordinary skill in the art. In a last step, in order to form a final unitary structure, this preliminary bonding is rendered more permanent by a high temperature and pressure lamination process known to one of ordinary skill in the art such as, but not limited to, autoclaving.
An emerging market in architectural laminated glass requires monolithic interlayers with structural properties. Such an interlayer is Eastman's Saflex DG which is made of plasticized polyvinyl butyral (“PVB”). A structural poly(vinyl acetal) interlayer, Saflex™ DG41 (a poly(vinyl butyral) polymer having an Mw of about 170,000, is commercially available for applications in the architectural space. Saflex™ DG interlayers are stiffer products than standard PVB interlayers and the higher stiffness allows laminates made with Saflex™ DG interlayer to sustain higher loads. Alternatively, Saflex™ DG interlayers can be used to allow a reduction in the glass thickness while achieving the same laminate loading.
Higher performance interlayers are desirable as more applications requiring such interlayers are growing (single side balcony laminates, canopies, staircases, support beams, etc).
To increase the stiffness of a thermoplastic, reinforcing fillers are often used. However, such solid fillers may not be thermoplastic polymers, and therefore can compromise adhesion to glass and/or its processability in an extruder. Where optical clarity is desired, such fillers are unsuitable if too large as they scatter light and reduce the optical clarity of a glass laminate. Smaller particles reduce the potential for light scattering but due to their high surface area, often increase the viscosity of the matrix thermoplastic resin, rendering processing difficult or impractical. There, there remains a need to increase the stiffness or rigidity using a thermoplastic polymer, and optionally maintain good optical clarity, of the laminates made with poly(vinyl acetal) interlayers while maintaining the ability of the thermoplastic poly(vinyl acetal) to process well. For many applications, the monolithic interlayer is desirable to decrease the thickness of the laminate, avoid the processing time of laying up multilayers, and decrease the failure rate of laminates off the line that have the formation of bubbles or imperfections due to faulty assembly of multilayers.